The present invention relates to multilamp photoflash units and, more particularly, to improved means and methods for providing electrical insulation between adjacent elements in compact multilamp photoflash units.
Numerous multilamp arrangements with various types of sequencing circuits have been described in the prior art; particularly in the past few years. A currently marketed photoflash unit (described in U.S. Pat. Nos. 3,894,226; 3,912,442; 3,935,442; 3,937,946; 3,941,992; 3,952,320 and 4,017,728 and referred to as a flip flash) employs high-voltage type lamps adapted to be ignited sequentially by successively applied high voltage pulses from a source such as a camera-shutter actuated piezoelectric element. The flip flash unit comprises an elongated planar array of eight high-voltage type flashlamps each having a pair of lead-in wires connected to a printed circuit board by means of eyelets secured thereon. The circuit board is provided with switching circuitry for causing sequential flashing of the lamps, and an array of respectfully associated reflectors are positioned between the lamps and the circuit board. The reflectors for the lamps can be made as a single reflector member shaped to provide multiple individual reflectors for the lamps. The reflector member preferably is electrically conductive, such as being made of metal or metal-coated plastic, and is electrically connected to an electrical "ground" portion of the circuitry on the circuit board. Thus the reflector member functions as an electrical shield reducing the possibility of accidental flashing of lamps by an electrostatic voltage charge on a person or object touching the unit. Such accidental flashing is particularly prone to occur in this instance as the lamps are high voltage types requiring a firing voltage of 500 to 4000 volts, for example, at low current.
Although an electrically conductive reflector is desirable, as has just been explained, care must be taken to prevent the reflector unit from shorting the circuitry on the circuit board, which is located immediately behind the reflector unit, thus preventing the circuit from flashing the lamps. According to the above referenced U.S. Pat. No. 3,894,226, Hanson, this problem is solved by interposing between the reflector unit and circuit board a sheet of electrically insulating material to prevent shorting of the circuitry on the circuit board by the conductive reflector. The insulating sheet may be of a transparent plastic a few thousandths of an inch thick, which transmits sufficient radiation from flashing lamps to actuate adjacent radiation switches in the switching circuitry, and also to actuate flash indicators located behind the circuit board. Typical method steps for assembling such a unit are as follows. First, the printed circuit board is provided with terminals, conductive runs, and radiation sensitive switches. Next, eyelets for holding the lamp lead-in wires are inserted through selectively located holes in the circuit board. The lamps are then mounted on the circuit board by inserting the lead-in wires into the eyelets and bending and crimping the eyelets. The back of the reflector unit is provided with a pair of locating studs which correspond with locating holes in the insulating sheet and the circuit board. Hence, in the next step, the insulating sheet is assembled to the reflector member by aligning the reflector studs with the locating holes in the sheet. The reflector-insulating sheet assembly is then joined with the lamp-circuit board assembly by passing the lamps through large openings in the insulating sheet (denoted 53 in the Hanson patent) and corresponding aligned openings in the reflector (denoted as 52 in the Hanson patent). Once the reflector-insulating sheet assembly is securely mated with the circuit board, with the studs of the reflector placed into the locating holes of the circuit board, the lamps, which had been substantially normal to the surface of the circuit board, are now bent over into the reflector cavities such that the lamp axes are substantially coplanar and parallel to the circuit board. Thereafter, the remaining portions of the unit assembly are completed.
The above-referenced copending application Ser. No. 840,497, Audesse et al., describes an improved multilamp photoflash unit which more efficiently utilizes a given housing volume and thereby reduces the cost of the unit per flashlamp contained therein. More specifically, a compact lamp arrangement is provided whereby additional lamps are contained in a given volume while maintaining light output performance requirements. In a particular embodiment described, ten lamps are provided in a housing having the same dimensions as the above-discussed eight-lamp flip flash units. The greater compactness is provided by arranging the planar array of lamps in two parallel columns with the tubular envelopes horizontally disposed and with the lamps of one column staggered with respect to the other such that the bases are interdigitated. A pair of reflector panels are aligned with the two columns of lamps and arranged overlie the lamp lead-in wires and bases.
As may well be appreciated, the above-described compact ten-lamp array imposes a significant challenge with respect to packing design and the lay out of a suitable sequencing circuit on the associated printed circuit board. In particular, the electrically sensitive circuit pattern is so dense on the lamp mounting surface of the circuit board, that the luxury of large openings in the transparent insulating sheet for facilitating assembly over the lamps can no longer be tolerated. In order to adequately provide electrical insulation between the conductive reflector members and the dense pattern of circuitry on the circuit board, openings in the insulating sheet must be keep to an absolute minimum. Hence, the insulating sheet must be placed on the sensitive circuit board surface prior to lamp mounting, with small holes provided on the sheet for passing the lamp lead-in wires into the eyelets on the circuit board for bending and crimping. Another difference in the assembly is that the lamps are mounted for being disposed horizontally in the finished array, whereas in the prior art eight-lamp array the lamps were disposed vertically, and two reflector panels, comprising the two halves of the total reflector array, are joined together from each side onto the lamp-insulator-circuit board assembly. There is no lamp-fitting hole in each reflector panel since the lamps are positioned directly into the reflector cavities as the panel is positioned on the insulator-covered circuit board. In view of the necessary changes in configuration and assembly procedures for the aforementioned compact photoflash unit, a problem arises as to how to maintain the critical alignment of the insulating sheet on the printed circuit board during manufacturing assembly on high volume, automated production equipment.